1. Field of the Invention
This invention generally relates to check valves, and more particularly to tide gate valves.
2. Description of the Prior Art
A check valve is essentially a valve which allows fluid flow in only one direction through a conduit, while closing and preventing back or reverse flow, when back pressure builds up downstream of the valve to a level greater than the upstream fluid pressure head.
One example where the fluid back-flow problem is especially acute occurs where such valves are used to handle raw sewage, sewer effluent and storm water. Virtually all municipalities near waterways have storm and sewer lines which empty into the water ways. When there is a storm, storm water from the streets runs into and through these sewer pipes and flows into the waterways. Sewage treatment plants discharge raw or treated sewage into the waterways. When the tide is in, these sewer pipes back fill with the water from the waterway. This leaves no or reduced storage capacity in the sewer pipes. In the event there is a large cloudburst or storm during the time that the tide is in, all or a portion of the storm water cannot get in the sewer because the sewer pipes are at least partially filled. This causes street flooding.
Another example where the fluid back flow problem is especially acute is where the check valves are used in chemical plants or municipal waste treatment plants. In such applications, it is desired to permit waste water or treatment chemicals to enter a reaction vessel or pond from a storage container without permitting the contents of the reaction vessel to back flow into the storage container as the chemical reactions proceed.
To deal with the back flow problem, particularly to prevent street flooding by storm sewers, various types of tide gate valves have been proposed. One type consists of a wooden gate which floats up when the tide comes in, thereby closing the tide gate valve to prevent the sewer pipes from filling with the tide water. When the tide goes out, the wooden gate sinks, thereby opening the tide gate valve. Another type consists of a mechanical tide gate valve made of steel. This type is subject to corrosion, which adversely affects its operation. Spring loaded valves having several moving parts also have been proposed but are unreliable in operation. Many of these prior art valves jam in the open position or otherwise fail to open or close when required. Noise, slamming or chatter are frequently prevalent with such types of check valves. Sliding, rotating, swinging and plunging parts lead to wear and failure or jamming, especially when handling slurries or other fluids containing entrained particulate solid material. Such previously proposed tide gate valves are also subject to jamming when trees, logs, bricks and the like get into the valves and prevent the gates from fully closing.
One check valve which has been developed in recent years is the duck-bill sleeve-type check valve. Such a valve entails a flexible, resilient sleeve which terminates with a symmetrically tapered duck-bill configuration and a rectilinear outlet end which opens to an oval or circular shape to accommodate successively greater fluid flow, but which closes on back pressure build-up.
One problem with such valves is that when a high back pressure is encountered, the valve's lips are prone to collapse and invert, thus permitting an undesirable back flow of fluid. This problem is intensified for large size valves on the order of 24 inches or even greater diameter, because the larger the diameter of the valve, the larger the area of the valve and, in such cases, even a relatively low back pressure will provide sufficient force to collapse and invert the valve's lips, thus allowing reverse flow or back flow of fluid to take place.
Another related design problem associated with the tide gate valve concerns the ease of opening the valve. The more one attempts to design the valve to resist inversion, the less easy the valve is to open. Thus if one constructs the valve with rigid materials, the valve will certainly resist inversion and sagging, but at the expense of making the valve much tougher to open. The reverse situation also is true. That is, if one constructs the valve with very flexible materials, the valve will open easily, but at the expense of resisting inversion.
Improved tide gate valves are disclosed in U.S. Pat. Nos. 4,492,253; 4,585,031; and 4,607,663.
A need remains in the art for a duck-bill sleeve-type check valve or tide gate valve which will open with a very low head pressure, wherein the valve can be made of thin and flexible materials, yet where the valve retains the ability to resist inversion during periods of high back flow pressure.